What is Diplontic Life Cycle?

Diplontic life cycle refers to the life cycle of organisms, which is dominated by the diploid stage. Plants and algae show alternation of generation. All the plants showing sexual reproduction alternate between two multicellular stages, viz. Haploid gametophyte and diploid sporophytes.

In the diplontic life cycle, the diploid stage or sporophyte is the dominant and independent stage of the plant and performs photosynthesis. The haploid phase is represented by single-cell gametes or few celled gametophytes.

Here mitosis usually occurs at the diploid stage, i.e. zygote and gametes are produced by meiosis.

Diplontic Life Cycle Examples

The Diplontic life cycle is shown by some algae and all the phanerogams or seed-bearing plants.

Brown algae Fucus has a diplontic life cycle. The main plant body is thallus, which is diploid. The haploid phase is represented by oogonia and antheridia, which are formed by meiosis in reproductive cells present in the conceptacles. Oogonia and antheridia produce egg and sperm respectively, which fuse to form a diploid zygote. The zygote (2n) divides mitotically to form thallus. Other algae which show the diplontic life cycle are green algae Cladophora and Acetabularia, diatoms, etc.

All the seed-bearing plants, i.e. Gymnosperms and Angiosperms show the diplontic life cycle.

Types of Biological Life Cycle

In plants, both haploid and diploid cells can divide mitotically and proliferate to produce gametophyte (n) and sporophyte (2n), respectively. Plants that undergo sexual reproduction, alternate between the haploid and diploid stages. This is known as alternation of generations.

Based on the dominant stage of their life cycle, they are categorized into three types:

  1. Haplontic Life Cycle – The dominant stage is the haploid gametophyte. The diploid sporophyte is only represented by the zygote, which is diploid. The zygote divides meiotically to form haploid cells, which undergo mitosis to form multicellular haploid organisms. Diploid stage is not free-living. Examples: Green algae, e.g. Volvox, Spirogyra, Chlamydomonas, etc.
  2. Diplontic Life Cycle – The diploid sporophyte is the dominant stage. It shows gametic meiosis. E.g. Gymnosperms, Angiosperms, Fucus, etc.
  3. Haplodiplontic Life Cycle – Here both haploid and diploid stages are multicellular. In some, the gametophyte is dominant and free-living and the sporophyte is a small and short-lived phase, which is dependent on gametophytes, e.g. Bryophytes.

In pteridophytes, the sporophyte is the independent and free-living dominant stage. It alternates with short-lived gametophyte.

Some algae such as Ulva, Polysiphonia, Ectocarpus, Kelps have a haplodiplontic life cycle.

Difference Between Diplontic and Haplontic Life Cycle

Diplontic Life Cycle

Haplontic Life Cycle

Sporophyte (2n)

Dominant phase, which is independent, free-living and performs photosynthesis

Conspicuous and represented by Zygote or few celled sporophytes

Gametophyte (n)

Conspicuous and represented by gametes, i.e. egg cell and sperm or few-celled gametophyte

Dominant phase, which is independent, free-living and performs photosynthesis

Mitotic Division

The zygote divides mitotically to give rise to a new plant.

Haploid cells divide mitotically to produce new plants.

Meiosis Division

Gametes are produced by meiosis division.

The zygote divides meiotically to form haploid cells, which proliferate by mitosis.

Examples

Angiosperms, Gymnosperms, some algae such as Fucus, Cladophora, etc.

Most of the algae such as Volvox, Spirogyra, etc.

This was all about Diplontic Life Cycle. Explore notes on Plant Kingdom and other important concepts related to NEET, only at BYJU’S.

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